//Given the root of a binary tree and an integer targetSum, return the number 
//of paths where the sum of the values along the path equals targetSum. 
//
// The path does not need to start or end at the root or a leaf, but it must go 
//downwards (i.e., traveling only from parent nodes to child nodes). 
//
// 
// Example 1: 
//
// 
//Input: root = [10,5,-3,3,2,null,11,3,-2,null,1], targetSum = 8
//Output: 3
//Explanation: The paths that sum to 8 are shown.
// 
//
// Example 2: 
//
// 
//Input: root = [5,4,8,11,null,13,4,7,2,null,null,5,1], targetSum = 22
//Output: 3
// 
//
// 
// Constraints: 
//
// 
// The number of nodes in the tree is in the range [0, 1000]. 
// -10⁹ <= Node.val <= 10⁹ 
// -1000 <= targetSum <= 1000 
// 
// Related Topics Tree Depth-First Search Binary Tree 👍 6517 👎 342

  
package leetcode.editor.en;

import java.util.HashMap;
import java.util.Map;

public class _437_PathSumIii{
    public static void main(String[] args) {
         Solution solution = new _437_PathSumIii().new Solution();
    }
    //leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int pathSum(TreeNode root, int targetSum) {
        if (root==null) {
            return 0;
        }
        Map<Integer, Integer> map = new HashMap<>();
        map.put(0, 1);
        return dfs(root, targetSum, map, 0);
    }

    private int dfs(TreeNode root, int targetSum, Map<Integer, Integer> map, int curSum) {
        if (root == null) {
            return 0;
        }
        curSum+=root.val;
        int res = map.getOrDefault(curSum-targetSum, 0);
        map.put(curSum, map.getOrDefault(curSum, 0)+1);
        res+=dfs(root.left, targetSum, map, curSum);
        res+=dfs(root.right, targetSum, map, curSum);
        map.put(curSum, map.get(curSum) - 1);
        return res;
    }
}
//leetcode submit region end(Prohibit modification and deletion)

}